In general, cutting tools include an indexable insert which is detachably attached to a tip portion of a cutting tool in order to perform a turning or planing operation for a workpiece such as made of various steels or cast irons, a drill or a miniature drill which is used for performing a drilling operation for a workpiece as mentioned above, and a solid type end mill which is used for performing a face milling operation, a groove milling operation, or a shoulder milling operation for a workpiece as mentioned above. In addition, an indexable type end mill is also known, to which an indexable insert is detachably attached for performing a cutting operation as in the case of the solid type end mill.
Moreover, as a coated cutting tool, a coated hard metal tool is known in which a hard coating layer, which has an average thickness of 1 to 15 μm and is made of TiN or a nitride compound (hereinafter termed (Al, Ti)N) layer that includes aluminum and titanium and satisfies a composition formula of (AlZTi1-Z)N (where Z indicates an atomic ratio of 0.4 to 0.65), is formed, using a physical vapor deposition method, on the surface of a substrate made of a tungsten carbide (hereinafter termed WC) based cemented carbide, a titanium carbonitride (hereinafter termed TiCN) based cermet, or a cubic boron nitride (hereinafter termed c-BN) based sintered material (hereinafter such a substrate is referred to as a hard substrate). It is also well known that such a coated hard metal tool is used in a continuous cutting operation or an interrupted cutting operation for various kinds of steels and cast irons.
Furthermore, it is also known that the above-mentioned coated cutting tool is fabricated through a method in which the above-mentioned hard substrate is accommodated in, for example, an arc ion plating apparatus schematically shown in FIG. 2, which is a type of physical vapor deposition apparatus, an electric current of, for example, 90 A is made to flow as an arc discharge between an anode electrode and a cathode electrode (an evaporation source) to which an Al—Ti alloy having a predetermined composition is attached under the conditions in which the inside of the apparatus is heated to a temperature of, for example, 500° C. using a heater, a nitrogen gas as a reaction gas is introduced into the apparatus so as to prepare a reaction atmosphere at, for example, 2 Pa, and a DC bias voltage of −100 V is applied to the cutting tool, so that a hard coating layer, which is made of an (Al, Ti)N) layer is formed on the surface of the above-mentioned hard metal substrate.
On the other hand, in order to improve sliding performance of a hard coating layer, a hard coating layer, as disclosed in, for example, Japanese Unexamined Patent Application, First Publication, No. H05-330956, has been proposed, which is made of a nitride compound layer (hereinafter termed (Ti, R)N) of Ti and a rare-earth element that satisfies a composition formula of (Ti1-ZRZ)N (where Z is within a range from 0.005 to 0.20, R indicates a rare-earth element such as Dy, Y, La, Nd, or Gd, and Z indicates an atomic ratio of the rare-earth element among the totality of the metal elements) using an ion mixing method.
In recent years, cutting operation apparatuses tend to have significantly high performance, and on the other hand, it is strongly demanded that cutting operations be performed with less power, less energy, and less cost; therefore, cutting operations tend to be performed at high speed. With regard to the above-mentioned conventional coated cutting tool, no significant problem is encountered when such a tool is used under normal cutting conditions; however, when such a tool is used under high speed cutting conditions in which a significant amount of heat is generated, wear of the hard coating layer of the tool is significantly progressed, which leads to a relatively short operation life.
Furthermore, in recent years, cutting operations tend to be performed under severe conditions such as with a large depth of cut or a large feed. With regard to the above-mentioned conventional coated cutting tool, no significant problem is encountered when such a tool is used under normal cutting conditions; however, when such a tool is used in an interrupted cutting operation under severe conditions, such as with a large depth of cut or a large feed, in which large mechanical impacts occur, a cutting edge tends to easily be chipped (small fracturing) due to insufficient strength and toughness of the hard coating layer, which leads to a relatively short operation life.